1. Field of the Invention
The present invention concerns a rolling contact bearing assembly, and, in particular, relates to a linear motion rolling contact bearing assembly having a particularly shaped retainer for retaining a plurality of rolling members in position.
2. Background of the Invention
A linear motion rolling contact bearing assembly is well known in the art, and, as shown in FIG. 1, it includes a table 1 which is typically formed by bending a thin steel plate to have a U-shaped cross section, a bed 2 which is also typically formed by bending a thin steel plate to have a U-shaped cross section and a plurality of rolling members or balls 3 in the illustrated case, interposed between the table 1 and the bed 2 thereby providing a relative motion between the table 1 and the bed 2. The table 1 has a U-shaped cross section and thus it has a flat base section and a pair of side wall sections upstanding on opposite sides of the flat base section. Similarly, the bed 2 is U-shaped in cross section so that it also has a flat base section and a pair of side wall sections. In the illustrated case, the table 1 is made larger in width than the bed 2 so that the table 1 straddles the bed 2 when assembled.
The opposed surfaces of the side wall sections of the table 1 and the bed 2 are formed with paired guide grooves extending in the longitudinal direction of the assembly, thereby defining a guide passage for guiding the rolling motion of the balls in rolling contact with the guide grooves. As shown in FIG. 1, also provided between the opposed surfaces of the side wall sections of the table 1 and the bed 2 is a retainer 4' for retaining the balls 3 in position as spaced apart from one another at a predetermined pitch. The retainer 4' is rectangular in shape and is provided with a plurality of simple holes as spaced apart from one another in a line. As also shown in FIG. 1, an upper end member 5 is fixedly attached to each end of the table 1, whereas, a lower end member 6 is fixedly attached to each end of the bed 6, so that the internal space defined by the table 1 and the bed 2 may be completely enclosed when the table 1 is placed in alignment with the bed 2.
When the table 1 moves relative to the bed 2 along the longitudinal direction of the assembly, the balls 3 also roll sandwiched between the paired guide grooves, and, thus, the retainer 4' also moves in the longitudinal direction. In this case, the retainer 4' is subjected to rather complicated movements, shown in FIG. 2, in which the intended normal position of the retainer 4' is indicated by the solid line; but the retainer 4' becomes inclined as a result of its rolling motion as it moves in the longitudinal direction of the assembly. The retainer 4' under the condition may be inclined as far as 5 degrees. When analyzing the motion of the retainer 4' during movement along the longitudinal direction of the assembly, it becomes clear that the retainer 4' is subjected to a rolling motion, which is the clockwise or counterclockwise motion of the retainer 4' around the ball center C, a translational motion, which is the horizontal motion of the retainer 4' to the left or to the right of the ball 3, a yawing motion, which is the vertical motion of the retainer 4' upward or downward due to the gap between the ball 3 and the retainer 4', and a pitching motion, which is the front and rear motion of the retainer 4' due to the gap between the ball 3 and the retainer 4'.
Since the prior art retainer 4' is subjected to these various motions, there are various disadvantages resulting therefrom. For example, if the gap between the ball 3 and the retainer 4' is large, the retainer 4' can be shifted sideways of the ball 3 so as to come in contact with one side wall of the table 1 or the bed 2, thereby increasing the resistance against the relative motion between the table 1 and the bed 2. Moreover, since there is a gap between the upper and lower end members 5 and 6, the retainer 4' may project out of the assembly as passing through the gap, whereby the retainer 4' often becomes stuck between the upper and lower end members 5 and 6. In addition, a lubricant cannot be distributed uniformly along the entire length of the retainer 4'.